1. Field of the Invention
The invention is concerned with the fabrication of integrated circuits.
2. Description of the Prior Art
Deposition and patterning of thin films of metals such as aluminum, gold, titanium and platinum on semi-conducting and insulating substrates are essential processes in the manufacture of integrated circuit devices. Deposition of metallic layers may be carried out directly by vapor deposition in a vacuum, and patterning by depositing on the metallic film an organic photoresist mask followed by chemical etching. To etch a pattern in a layer of gold by this method it is necessary to use aqua regia as an etchant which, however, tends to lift the photoresist material form the gold layer. As a consequence, pattern definition suffers.
A method specifically directed to making a patterned gold film was described in U.S. Pat. No. 3,684,569, issued to A. A. Milgram on Aug. 15, 1972. Milgram proposes the use of ultraviolet light to selectively influence the hardening of a deposited film of gold resinate, removal of exposed portions of the film by means of a solvent such as nitric acid, and heat fusing the patterned gold resinate to metallic gold. Another method is described in U.S. Pat. No. 3,056,881, issued to H. J. Schwarz on Oct. 2, 1962. Schwarz proposes to delineate a pattern in a layer of a tightly bound metal oxide such as Al.sub.2 O.sub.3 by means of a programmed electron beam and in the presence of a reducing agent, thereby locally reducing the metal oxide to elemental metal.
It has been ascertained, however, that Al.sub.2 O.sub.3 cannot be reduced by electron irradiation at practically feasible energy levels. It has been further ascertained that metal oxides which are susceptible to reduction of the metallic state by electron irradiation are likely to dissociate under conditions occurring during the operation of integrated circuit devices. Consequently, the mere delineation of a metallic pattern in a film of a compound susceptible to reduction by electrons does not yield practically useful devices.